1. Field of the Invention
The invention relates to a method and a device for operating a premix burner.
2. Discussion of Background
Combustion chambers with premix burners which are designed as so-called double-cone burners and in which the fuel is supplied from the outside by plug-in fuel lances have long proven suitable for stationary gas turbines in power plants. The lance is generally configured as a two-fuel lance, i.e. it is possible, as desired, to supply gaseous fuel, e.g. pilot gas, and/or liquid fuel, for example an oil/water emulsion. To this end, a liquid-fuel pipe, an atomizer pipe and a pilot-gas pipe are arranged concentrically in the lance. The pipes each form a duct for the liquid fuel, the atomizer air and the pilot gas, which ducts, at the lance head, end in a fuel nozzle. The head of the fuel lance projects into a corresponding inner pipe of the double-cone burner, so that the fuel emerging passes via the fuel nozzle into the burner inner chamber which adjoins the inner pipe (cf. DE 43 06 956 A1).
EP 0,321,809 B1 has also disclosed a double-cone burner which is provided for use in a combustion chamber which is connected to a gas turbine. This burner comprises two hollow part-cone bodies which complement one another to form the double-cone burner and are arranged radially offset with respect to one another. It has a hollow-cone-shaped inner chamber which increases in size in the direction of flow and has tangential air-inlet slots. The fuel is supplied to the double-cone burner from the outside via the plug-in fuel lance which opens out into a liquid-fuel nozzle. The latter forms a hollow-cone-shaped fuel spray, consisting of liquid fuel and air, in the burner inner chamber, in which spray most of the fuel droplets are concentrated at the outer end of the conical spray pattern. Owing to the large spray angle of approx. 30.degree. and the absence of an axial impulse in the center, these sprays are highly susceptible to centrifugal forces which are generated by the turbulent flow in the interior of the burner. As a result, the fuel droplets are carried relatively quickly outward by centrifugal forces, resulting, under certain operating conditions, in a not insignificant quantity of the liquid fuel striking the inner walls of the burner.
So-called plain jet orifices for the atomization of liquid fuels are known from the text book "Atomization and sprays" by A. Lefebvre, West Lafayette, Ind. 1989, pp. 106/107, 238-240. In such atomizer nozzles, the liquid fuel is ejected, at high pressure and with a cone angle of from 5 to 15.degree., from an antechamber through at least one circular injection opening of a defined guide length. The disintegration of the fuel jet into individual drops is promoted at a high flow velocity, since as a result both the level of turbulence in the jet flowing out and the aerodynamic tensile forces exerted by the surrounding medium increase. The plain jet orifice described likewise injects the liquid fuel together with the water, so that the abovementioned problems with fuel distribution may equally well occur.